1. Field of the Invention
The present invention relates to a color image output apparatus and method for outputting a color image onto the printing medium by having the image data supplied, and in particular to an image output apparatus and method of the so-called serial scan type of outputting an image while scanning a print head along a predetermined direction relative to the printing medium.
Also, the invention relates to a method for effecting the print coloring on the cloths based on an ink jet system by the use of the heat energy.
2. Related Background Art
Color image output apparatuses for outputting a color image onto the printing medium with the image data supplied can perform the printing using print agents (color toner, color ink) of four colors of subtractive primary colors i.e., cyan (C), magenta (M) and yellow (Y) and black (Bk) to reproduce vividly three subtractive primary colors or black.
Also, image output apparatuses are in some cases desired to use other color print agents than the above colors of C, M, Y and Bk (hereinafter referred to as specializing color, e.g., metallic color or cobalt blue). This occurs when a color which is unable or difficult to represent with C, M, Y, Bk is required in the output image, or when the use of coloring agent such ink or toner is to be reduced.
In particular, in the fields of textile printing to be made on the cloths or gravure printing for posters, it is strongly demanded to reproduce faithfully the designs created by the designer, and therefore the use of print agents for specializing colors is desirable for the colors which can not be represented with C, M, Y, Bk.
On the other hand, it is often desired to have a higher print density or more print gradations.
Also, some images may be printed only using part of the print colors without requiring all the print colors.
In this way, along with the spread of image output apparatuses or extended application fields, various requirements for the image output apparatuses are raised, whereby it is strongly desired to provide image output apparatuses capable of minutely coping with such requirements, with less decreased throughput.
For example, when the higher print density is sought in the textile printing relying on the ink jet system, the inks for use with the textile printing have already high color densities, and still higher density will result in greater ink viscosities, whereby there is a risk that there occurs a trouble in the ink discharge. Also, if the optical density is to be increased by providing a greater dot diameter, the size or mass of ink droplet to be discharged may not become uniform, resulting in deviated shot positions, whereby there is a risk of producing streaks or unevenness in the connected portions of images, or producing white streaks in the portion on which even density should be expected. Further, apparatuses of scanning the print head across the same print surface multiple times to effect higher print density can not avoid the print speed decreasing.
Typical of the conventional coloring methods is a screen textile printing of using a silk screen plate to make the printing directly onto the cloths. The screen textile printing is a method in which for an original image to be printed, a silk screen plate is prepared for each color used in the original image, and the ink is directly transferred through silk meshes onto the cloths to effect the coloring.
However, such screen textile printing method has the problem associated therewith that many processes and days are required in fabricating screen plates, and the operations such as the proportion of color inks required for the printing, and the alignment of screen plates for color inks, are necessary. Moreover, the apparatus is large in size, and becomes larger in proportion to the number of used colors, requiring a larger installation space, and further the storage space for silk screen plates fabricated.
On the other hand, ink jet recording apparatuses have been put to practical use, which have the functions of a printer, a copying machine or a facsimile apparatus, or are useful as the output unit of a composite electronic equipment including a computer or a word processor, or a work station, and to solve the above problem, a number of recording methods have been proposed to employ such an ink jet recording apparatus for the color printing of discharging the ink directly onto the cloths.
With such methods, there is no need for plates used for the screen textile printing, so that the processes and days before the printing onto the cloths can be largely shortened, with the reduced size of apparatus. Naturally, since the image information for printing can be stored in a medium such as a tape, a floppy disk, or an optical disk, the excellent storage or preservation ability can be attained. Further, the change in coloration, layout change, enlargement or reduction of original image can be readily effected.
In particular, ink jet recording means (recording head) of discharging the ink by the use of heat energy can be easily fabricated having an arrangement of liquid channels (arrangement of discharge ports or orifices) with high density by having electricity-heat converters, electrodes, liquid channel walls and a ceiling plate formed as films on the substrate through the semiconductor fabrication processes including etching, vapor deposition and sputtering, thereby allowing for further compact constitution, higher recording speed and higher definition in image quality, and this method is expected as one of the coloring methods on the ink jet print system.
The inks for use with a special ink jet printing method such as textile printing are subjected to more severe requirements than with the conventional ink jet recording onto the recording medium such as paper, including:
Sufficient density for the coloring PA1 No clogging in ink discharge orifices or ink channels of head PA1 Less irregular blur on the cloth PA1 No change in discharge characteristic despite durable uses over the long term, in particular, no deposition of foreign matters on the heater for applying the heat energy, or no heater breakage due to cavitation at the extinction of bubbles, in the type of discharging the ink by the use of heat energy. The inks which can meet the above requirements have been proposed in the inventions such as Japanese Patent Publication No. 62-57750 and Japanese Laid-Open Patent Application No. 61-179269.
However, in the state of the art, none of the ink jet printing methods have been known which can satisfy all these performances simultaneously, although partially meeting individual performances to some extent.
Further, a new problem as will be described later has arisen in attempting to put the ink jet printing method to practical use.
Among the apparatuses for use with the ink jet printing, a serial type apparatus relies on the serial scan method of scanning in a direction crosswise to the conveying direction (sub-scan direction) of the recording medium. With this apparatus, the printing of an entire image on the recording medium is achieved in such a way as to repeat the recording operation of printing one line of image by recording means mounted on the carriage movable in a scan direction over the recording medium, feeding the sheet (pitch convey) by a predetermined amount in a sub-scan direction after one line of recording, and then printing the next line of image onto the recording medium as positioned.
In order to put this ink jet printing apparatus to practical use for the color printing, the continuous print length (scan length) must be much longer (approximately 0.6 m or more) than with the normal ink jet recording apparatuses as the printers, owing to the requirements from the production speed or with the final products such as clothings. For this reason, in the ink jet printing method of discharging the ink from the head by the use of heat energy generated by heat generating elements of the head upon the application of a drive signal, the head temperature greatly rises, because of its scanning over the longer length to be performed at one time, whereby it is difficult to maintain a stable discharge during one time of scanning, owing to largely changing ink viscosity. As a result, the ink likely may not be discharged.
Further, the depositing amount of ink mist onto the head orifice face will be quite enormous, as may occur at the ink discharge due to the longer scanning for one time, causing a clogging of nozzle orifices which will lead to undischarge (wetting undischarge). Further, even the ink mist deposited in the neighborhood of nozzles is swept away over nozzle openings by contact with the fiber such as fluffs or waste threads present on the surface of cloths, causing a clogging of nozzle which will lead to undischarge of the ink. Also, there occurs a new problem that waste threads themselves as above described may clog any of the nozzle openings because there are more chances of making contact with and attaching onto the nozzle openings, thereby causing undischarge. This is a remarkable problem which may occur with the apparatuses having a longer print length, such as those of discharging the ink by the application of drive signals as many as 5.times.10.sup.3 times or more in one scan through at least one of the nozzles of head.
If an image is able to be directly formed on the cloths by using the ink jet recording apparatus as above described, instead of the conventional textile printing method as previously described, the number of processes or days required for the image formation on the cloths can be greatly shortened without need of the screen plates, and the smaller apparatus can be fabricated. However, in the case of using the cloths as the recording medium, there is a problem that the coloring ability or image density may be degraded, unlike the case of recording onto the paper. Therefore, only the standard colors, normally consisting of four colors (cyan, magenta, yellow and black) for use with the full-color recording onto the paper, was difficult to cover a sufficient range of color reproduction in the case where the printing is made onto the cloths. Thus, a technique has been proposed in which other colors than the four standard colors are employed as specializing colors, such inks of specializing colors used together with the standard color inks.
However, when the specializing color inks are additionally used with the standard color inks, it is necessary to increase the number of recording heads depending on the kinds of used inks, thereby often resulting in too large a head holder for holding the recording heads. As a result, even when the recording heads for specializing colors are provided but are not used, it will take more time to effect the printing operation or recovery operation (wiping, idle discharge) which is intrinsic to the ink jet recording system, resulting in a problem of the substantial decreased recording speed.